Feedback In Loudspeakers

EE 20 April 1987 FEEDBACK IN LOUDSPEAKERS by R Conell Electrical feedback is the backbone of many an electronic circuit. Acoustic feedback is not nearly so common, but R Conell suggests some ways of experimenting with it in a low-frequency loudspeaker. Ever since Thiele and Small published their works on loud- speaker theory, it has been possible to calculate fairly ac- curately what the ideal enclos- ure is for a certain type of loudspeaker, or conversely how a loudspeaker will behave in a certain enclosure. Accord- ing to Small, a closed box will behave as a second-order high- pass filter, while Thiele shows that bass reflex and trans- mission line boxes act as fourth- or sixth-order filters. From this it is clear that a closed box will give better bass reproduction than an open system. The performance of a filter is determined by its quality factor Q and its resonance frequency f. This is also true of a complete loudspeaker system, including the enclosure, when the total Q is d...